152 BACTERIOLOGY. 



3. The vegetative development of the organisms is 

 destroyed, but not the spores incomplete sterilization. 



4. Vegetative and spore-formation are destroyed. 

 This is complete sterilization or disinfection. 1 



The methods employed for the determination of the 

 germicidal action of chemical agents on bacteria are, 

 briefly, as follows: 



If it is desired to determine what is the minimum con- 

 centration of the chemical substance required to produce 

 complete inhibition of growth we proceed thus : A 10 

 per cent, solution of the disinfectant is prepared and 

 1 c.c., 0.5 c.c., 0.3 c.c., 0.1 c.c., etc., of this is added 

 to 10 c.c. of liquefied gelatin, agar, or bouillon, or, 

 more accurately, 10 c.c. minus the amount of solution 

 added, in so many tubes. The tubes then contain 1 per 

 cent., 0.5 per cent., 0.3 per cent., and 0.1 per cent, of 

 the disinfectant. The fluid med a in the tubes are 

 then inoculated with a platinum loopful of the test 

 bacteria. The melted agar and gelatin may be simply 

 shaken and allowed to remain in the tubes, and watched 

 as to whether any growth takes place, or the contents 

 of the tubes are poured out into Petri dishes, where the 

 development or lack of development of colonies and 

 the number can be observed. The same test can be 

 made with material containing only spores. 



If it is desired to determine the degree of concentra- 

 tion required for the destruction of vegetative develop- 

 ment, the organism to be used is cultivated in bouillon, 

 and to each of a series of tubes holding in watery 

 solution different percentages of the disinfectant a 



1 Disinfection strictly defined is the destruction of all organisms and their 

 products which are capable of producing disease. Sterilization is the destruc- 

 tion of all saprophytic as well as parasitic bacteria. Practically, however, 

 the two terms are used interchangeably as meaning the destruction of all 

 living bacteria. 



